The practice of being esoteric is called esotericism. There are three main categories of esotericism: religious, philosophical, and occult. Information that is only understood by a small group is said to be occult esotericism. Only a select few who have interest or knowledge in the information are able to understand it. These groups of people only share their knowledge with a small group of people and can also be interested in items that are rare and unique.
This particular definition of esoteric was found in numerous places such as Pythagoreanism, Buddist and Hindu Tantra, Anicent Egypt, Radhasoami, and in Hermetic Occultism. There is no thread that ties the history of esotericism to its origins. Conflicts arise whether to view esotericism in a scholarly or non-scholarly sense. Esoteric doctrines can be tied to great scholars such as Lucian or Aristotle. You can download free pdfs ancient history esoteric from these classic scholars by doing an internet search.